To spin up a new stack you can run the creat.sh followed by the stack name
./create.sh udacity-project-2
The script takes params.json and changes the stack name to what you have specified above, in this case udacity-project-2
The script will then create a latest-params.json and uses that to deploy the stack.
When the stack has been created you can access the web application via the load balancer hostname.
You can find the load balancer hostname in the outputs section of the stack in the AWS CloudFormation Web Console.